1. Field of the Invention
The present invention relates to a network system transmits/receives data frame among nodes connected to a network according to a predetermined protocol, and mutually diagnosing operational abnormality of nodes.
2. Description of the Related Art
High functionality, high performance, high reliability, high safety and enhancement of comfort of vehicles have recently provided the setting for increase of the mount number of electrical components of a vehicle, and the amount of information to be transmitted/received among electrical parts mounted in a vehicle has rapidly increased. Therefore, for the purpose of reducing the number of wire harnesses for transmitting information, a multiplex communication system (CAN (Controller Area Network) or the like) has been mainly adopted.
In the multiplex communication system, control ECUs as nodes for transmitting/receiving data frames are connected to a common multiplex communication line to form a network, and data communication is performed through the multiplex communication line among the nodes. In the case of a vehicle having a wide variety of control types, in order to perform data communication efficiently, nodes are classified into plural node groups which are different in attribute of communication speed to form plural networks, and the communication between different networks is performed through a data relay device.
Each ECU is normally constructed so as to be reset by a watchdog timer, and CPU monitoring based on only a watchdog timer system in which CPU is reset to avoid operational abnormality caused by runaway of CPU when CPU runs away goes mainstream. Safe performance has recently leveled up more greatly, and there is developed a control device in which the operation of CPU is monitored by mounting a large-scale integrated circuit (LSI) or the like in ECU so that CPU can be also reset when CPU fails in operation or the like.
Furthermore, in connection with the level-up of the diagnosis function, means for storing, into a backup memory or a non-volatile memory, freeze frame data for storing an operation state such as the rotational speed of an engine, a vehicle speed, etc. when a failure judgment is settled, ECU calculation status data when an ECU calculation error occurs, etc., thereby making it easily to analyze a source of subsequent failure has been recently adopted as general control.
In the case of a vehicle in which control contents are particularly complicated and the number of nodes is large, it is not easy to specify a source of failure when the vehicle breaks down or goes wrong due to deterioration of ECU or the like. Furthermore, the reset of ECU described above occurs not only due to failure of ECU itself, but also due to variation of a power supply or the like. In order to discriminate the reset caused by node abnormality such as failure or the like and the reset caused by the variation of the power supply, for example, JP-A-2002-44101 (pages 5 to 10, FIG. 1) discloses a node diagnosis method and a node diagnosis system in which a relay device as one node among plural node groups different in the communication speed attribute diagnoses failure of nodes, and it is made easy to specify abnormal node.
However, these techniques described above have a problem that the cost of ECU increases because a large-scale integrated circuit (LSI) or the like is mounted in ECU and also with respect to CPU reset based on monitoring LSI, CPU itself cannot detect abnormality.
Furthermore, according the technique described in JP-A-2002-44101, the reset frequency of abnormality-occurrence target ECU is counted and compared with those of the other nodes, and node abnormality is judged only when the count value is an excessive count value. That is, the reset frequency of the judgment target node is relatively compared with the reset frequencies of the other nodes, and it is judged whether the judgment target node is abnormal or not. Accordingly, the abnormality of the judgment target node cannot be judged with high precision. Furthermore, it cannot be recognized that reset occurs in the judgment target node itself when power supply to the judgment target node is interrupted, so that the abnormality cannot be judged with high precision.
For example, shock of a vehicle body, sudden engine stall or the like due to combustion failure of the engine under running may be caused not only by failure or deterioration of an engine constituting part such as a fuel system, an ignition system or the like, or failure or deterioration of an actuator or a sensor used to control ECU, but also by abnormality of a wire harness connected to ECU. Furthermore, these symptoms may also occur even when CPU operation of ECU fails or the power supply line is temporarily interrupted. In the instantaneous symptoms based on the temporary factor of ECU as described above, particularly the ECU reset during the idling state causes engine stall because fuel injection or ignition output is interrupted until the reset is restored. In such a case, a driver has a sense of mistrust and thus makes a claim.
Furthermore, the failure judgment is not settled in most cases because the symptoms are temporary. Therefore, it is difficult to store freeze frame data, operation status, etc. and it is not easy to specify a failure place in most cases.